Speed-indicator.



N. TESLA.

k SPEED INDICATOR.

APPLICATION FILED DEc.1 s.191s.

Patented A110. 6, 19181..

Illl llllll lIllllllI Imi) lig) NIKOLA TESLA, OF NEW YORK, N. Y., lA SSIGNOIR. T WLTHAM WATCH COMPANY, OF 'WALTHAIIL MASSACHUSETTS, A CORPORATION OFTMASSACHUSETTS'. l

1,274,816. Spammers raient. Patenten Aug; c, asia.v

A ppiication' med December 1a, 191e. semina. 137,691.

ments respectively adapted to measure relatively high and' .low speeds, but nevertheless 1t 1s ltrue that although such instruments,

ToaZZ whoml t may concern.'

Be it known that I, NIKOLA TEsLA, a citizen of the United States, residing at New l York, in the county and State of New York, whenebuilt for high-speed indication, may

5 have invented certain new and useful Imbe of sturdy construction, fthey must, when provements in Speed-Indicators, of which l'designed for lowspeed measurement, be the following is a full, clear, and exact debuilt with ,great wprecision and delicacy. scription. This because the inertia of. the secondary Among the desiderata of speedometer conelement must be kept extremely small for 6o 10 struction are these: that the torque exerted desirable promptness ,of response to very upon thel secondary, or indication-giving, slow starting speeds and consequent feebleelement shall be linearly proportional to the` ness of the turning effort. In some inspeed of the primary member rather than stances, therefore, it is highly desirable to to the squarevof the speed (as instanced in employ a transmitting medium Agiving a 65 'centrifugal speedometers) that the tormuch greater torque than air with concomisional effect at low speeds shall be strong' tantextension of the low-range of accurate and steady so that particular delicacy' of speed reading, quickness of response, prac'- construction may not be necessary and that ticable decrease of size of parts and lessenminute causes of theoretical errors (such as ing of sensitiveness 'to disturbances such as 7o bearing-friction, spring-inequalities andthe vibration ofthe instrument as a whole.

- like) may be negligible-in effect; 'that the. All of the stated objects I accomplish by torque ymay be substantially unaffected by employing as' the torque-transmitting rne-Y 'changes of extraneous conditions, as of temdium between the driving and driven' eleperature, atmospheric density and magnetic ments a body of suitable'liquid, (e. g., mer- 75 influence; that theinstnumentbe inherently cury) under conditions (as set forth in my dead-beat and relatively insensible to 'reprior application referred to) proper to chanical vibration;v and that ruggedness, secure linear proportionality ofdeflections, simplicity and economy, for attendant dural. and, further, by makingprovision automatibility, manufacturing facility 'and low cost, cally to compensate for the changes in the 80 30 be attained. My present speedometer real- Viscosity of the liquid thataccompany variaizes these advantages and provides, also, an tions of temperature. ,The latter equipment appliance that vis suitable for great, as w ell is unnecessaryl in my airldrag speedometer, as very small, velocities, exact in its read- \but mercury and other liquids of relatively ings, uniformly graduated as to scale, and great,4 density that might be employed for 85 unaffected by changes of temperaturek or. -my present purposes have not the quality pressure within as well as without. lof approximate self-compensation for temf. 5., In my .PatentlNa 1,209,359'dated Decemperature changes'that iii-heres in air, owing c vi 1 flber .519, 1916, I have described a new'type to thefact that the viscosity of such a liquid fof speed'measuringinstrumentl wherein the decreases rapidly as its temperature' rises, 90 4Q" adhesionand viscosity-of a gaseous medium, :and so to a successful mercury-drag? in# preferably air, is utilized "for torque-transstrument temperature compensationis reqmissionfrom a'primary driving to a second` uisite. y j Y. w ary pivoted'and torsionally restrained memY The underlying Yideas of this invention ber-unde conditions such'tliafl the rotary canv be carried out in various ways and. are. 95 4b effort exerted upon the' latter is linearly procapableof many fvaluable uses, but for? purportionalto the rate of 'rotation ofythe forposes of .disclosurewspecific reference to a mer. The principles of that inyention find form of speed indicatordesigned for use on v lplace in mypresent construction. Such air anautomobile is "adequate.

. dragspeedometers have been found capable As inthe structure described 1n my stated 10 0 application, y, yI provide driving and' membei'sf'witli' confronting, closelydriv n of.meetlngsatisfactorily the commercial reql irements for both large and small instruadjacent, non-contacting, smooth, annular friction surfaces, o o-acting for transmission of torque throughd the viscosity and adhesion of interposed thin lms of a suitable medium-in this case mercury-under condi- A tions to prevent. free exchange of fluid acting -lon the system, to

prevent its local circulation and eddying, to maintain its fiow calm and non-turbu`lent,"and to secure as low velocity of the medium with respect to the system as the circumstances of the case may make desirable. These conditions all aid in the attainment of rigorous linear proportionality of.' deflection ofthe secondary to the speed oflrotation ofthe primary element under given temperature conditions. Additionally, by suitable construction 1 make it'` possible to obtain a nearly perfect compensation for temperature changes so that the deflections may be rigorously proportionate to speed Within limits of temperature variation wider than ll believe likely to occur in the practical use of the instrument. 1 atresult by providing thermo-responsive means to vary the effective area of the ,secondaryelement upon` Whichthe medium acts in approximately inverse proportion to changes of VViscosity of the medium, and as a preferred specific means to this end, 1 dispose a body of the liquid beyond, but communicating with, the active portion of the liquid medium and of 'such quantity that, in effectively thesame measure as viscosity and, consequently, thev torque is diininished or increased with) temperature changes, theactive liquid-contacting area of the secondary member' is enlarged or reduced owing to the expansion or contraction of the Huid. r. 1 lin the drawing Figure 1 isa top View of a speedometer; f j

Fig. 2 is a central vertical section therethrough;

Fig. 3 shows .aspringA adjusting arrangement; and

Y 16, connected at it-sf that by Fig. 4C and'Fig. 5 arekdiagrams explanatoryof the compensatingprinciple. In 4 the primary or driving member -is a cup-:10 carried by a freely rotatable vertical shaft 11. Within it *the cylinderformed secondary me ber 12 is mounted on a spindle 13, journale in jewels 14 and 15 of negligible friction, for pivotal ldisplacementfagainst the restraint of a spiral spring ends respectively to fixed support 17 and spindle-collarj '18, so

pivotal displacement of the secondary cylinder aggainst the resisting spring tension, the torsional 'effort exerted on the secondary member` maybe measured. The spring iis -such that its displacements are inearly proportionate to the force ap lied. Thelower :portion 19, of the cup-chamberA is temperature-eccted change of temperature,

- have ascertained, can

' tionless). 1t will conditions .the activearea Will increase as i' [the volume ofthe fluid.4 Perfect compensay Lamela a reservoir lled with the liquid, 20, as merce cury, and the liquid normally extendsl part way up the very narrow interspace21vbecontact with less tween the'two elements to than the whole of their confronting friction .0.05 inch to be satisfactory.

1t will now be seen that when shaft '11 is rotated the mercury in the' cup is entrained and in turn produces v a drag upon the pivoted member 12, the torsional eH'ort being directly proportionate to the active area, viscosity of the fluid and the speed of rotation and, inversely, to the Width of the interspace 21 or distance betweenthe rotated and pivoted surfaces. 1f v be coefficient of viscosity, A the active area, sI the speed and d i the distance between the Juxtaposed lrotating and pivoted surfaces, all of thequantities twisting force F gdm dynee.y

the fluid expands thereby enlarging the areas of the active, or liquidcontracting, surfaces of the elements with an attendant increase of rotary eiiort. Obviously, then, if it is possible so `to relate these actions that they mutually annul each other upon any sation Vmayv` be obtained.4 This result, l(

be almost perfectlyv realized with a liquid, as mercury, by properly proportioning'the volume of the chamber-contained, or compensating, component 20c 'f the liquid and the cmponent 2Ol of the -liquid in the interspace 21. With a view to simplifying this explanation, be it supposed that the force F is wholly due tothe liquid component 20al (the drag exerted on the bottom face of cylinder 12 being assumed to be negligible and the bearings to be,V fricf evident that 'under these tion would require that upon a rise of tem- `perature, the active area, and therefore the torsional effort, lie-augmented in the same ratio as viscosit 'is diminished. In other words, the percentage of decrease of viscosity divided by that should be the same for alli temperatures. Attention is called to the table below showing that, with nierur as the medium, ,the

being expressed in proper units, then the ic@ a complete vcompentot ofi-increase of area value of this fraction atordinary temperatures is about, or not far from, 20.

Percentage Percentage Tempera Volume Viscosity Value of me o. 010010. 0101110. icfse "fcfase ratio.

i T V v a b 5 1I000909 0010003 0.0909 1.9107 .21102 1 i3 333433? 3333333 33333 37633 i333 This means to say that if the total volume of the liquid is twenty times that contained in the "interspace between the elements, the two opposite effects, one increasing and the other reducing, the torque, will approxivmatel balance. `This fact is borne out by practlcal tests and measurements, which have demonstrated that by constructing for this volumetric ratio defiections very closelyl proportionate to the speed are obtained through a range of temperature variations far greater than ordinarily occurring. For

commercial purposes it is quite suiiicient to employ a ratio of approximately the stated value as the error involved in al small departuretherefrom is inconsiderable. When necessary or desirable, greater precision can 'be obtained by taking into account four secondary effects, due to expansion or contractorque; first, changes in lthe volume of the reservoir; second, in the distance between the opposed surfaces; third. in active area and, fourth, `in `.velocity. Increase in the formertwo tend to diminish, the latter to augment, the viscous drag. A satisfactory ratio in a'c'ylindrical type of instrument has been found to be about 24.

Fig. 5 illustrates a different arrangement, exemplifying the same principle of employing a reservoir-contained liquid body as the thermo-responsive means to compensate for viscosity changes of the active'liquid. l In this case a spindle-'carried disk 12 serves as a secondary element, ',while the primary member consists of a hollow shell 10 with 1 annular surfaces 23 4confronting the disk Asurfaces and encompassed by an annular chamber 20', so that under rotation the mei'.

cury body fills the chamber and occupies peripheral Vportions of the interspaces 21 between the at confronting surfaces.. It

is lhardly ynecessary to remark that since there are two such interspaces 21, the calmoving parts.

tion of the walls, which slightly modify the culation of capacity of the reservoir or chamber 20,-beside considering the form of the device, must take account of the active mercury body in both interspaces.

' vIn Figs. 1 to 3a complete commercial instrument embodying my invention is shown.

Specifically, 25 is a tube threaded at 26 and carrying at the top a casing head 27 the whole forming a housing for inclosure of the The driving. shaft 28 carries a cylindrical cupl 29 in the bottom of which is screwed aplug 30, turned down as 31 for the purpose of providing thereservoir 32. rlhe cup 29 is closed, at its upper end by a tightfitting cover 33, having an upwardly' extending shank 34, carrying a pinion 35 to 80 drive suitable'wheelwork 36 of the odometer contained in the `lower part of the head 27.

This structure, providing the primary element, is rotatable in ball-bearings 37 and 38 fixed in tube 25 and adjustable by means of nuts 39.

The secondary element is made of a Very. thin metal cup 40, inverted and secured tov slender spindle 41 mounted in jeweled bearings 42 and 43, respectively `carried in a' cavity of plug 30 and by a frame arm 434.

A running bearing 42 can' usually be eml ployed without detriment,but a fixed bearing may be used if desired. v'llheweight of the secondary member with its 'movable attachments should 'be so determined that the upward thrust against jewel 43 is very slight. The torsional twist of secondary cup 40 is resisted by a spiral spring 44 lodged ing one of its ends connected to collar 46 in a turned recess ofa frame plate45, hav

lfast on the spigldle 41 and the other to. ay A vsplit ring 47 'spring-gripping" the wallof the recess in plate 45. By inserting pincers in holes 48 (Fig. 5) and contracting the ring it is vfreed suiiciently for adjustment to bring vthe spindle-carried indicator y49 to point to zero ofthe graduated scale 50 that,

if all of the principles of my invention are f best embodied, may be made uniformly graduated. AThe scale is carriedv on plate 45 and, together with the support 43', is

held lin place by a rim 53 that suitably Acarries the glass cover 52. The odometer may`- have any suitable number of indicating elements of diHerent orders suitably geared, the two hands 54 and 55 swee ing over graduated dials 56 and 57, typi ying any suitable construction.

It will be apparent thatthehigh -torque at low speed developed through the mercurial transmitting medium makes the instrument very eective as one for use on automobiles, and while it is'true that with a heavy fluid, as mercury, the range of ve-v locity of the mediumv throughout which proportionality of torque to speed, under the described conditions, is rigorously linear falls below-the range available where air is -the medium, a-construction presentingthe friction surfaces of the elements in a cylinder-form as suggested in Figs. 2 and 4 permits of the use of a suitably constructed devicel with a small-diameter secondary to measure very high speeds Without imparting that the mercury be pure, the surfaces contacting therewith smooth, clean and nongranular (preferably nickel-plated'or made of non-corrosive, high grade steel) to minimize abrasion Aand keep the mercury clean,

l.and that the linear velocity of themercury be kept low, preferably below six feet per second, in order that it may not break up into minute droplets or apparently-powdered form.

What l claim is: l j l. In combination, driving and driven elements, having opposed, closely-adjacent, non-contacting frictionpsurfaces; a liquid, body interposed between active areas thereof through which the driving element fric i driving andv movement-resisted driven eletionally drags the driven one and thermoresponsive means for varying the active .area 'of the secondary in approximately inverse proportion to the thermo-eected variations in viscosity of Ithe liquid. l A

2. ln a temperature-compensating speed indicator, the combination of variable speed primary and movement-restrained secondary elements that arel suitably supported for separate movement and have opposedfriction surfaces in close but non-contacting juxtaposition; an interposed liquid body 'contacting normally Awith active areas of said surfaces less than the whole thereof, and thermo-responsive means for varying the liquid-contacting areas of said elements approximately inversely to the thermoeected variations of liquid viscosity.

3. ln a temperature-compensating speed indicator, the combination of variable Speed primary and movement-restrained secondary elements that are suitably supportedV for separate movement and have opposed closelyadjacent non-contacting friction surfaces;

an interposed liquid body and thermo-re- For the successful use ofl invasie sponsive means for varying the active areas of said surfaces inv predetermined 'proportion to thermally-e'ectedychanges ofgliquid viscosity.

dit'

4.- lfn' a temperature-compensating" speed' indicator, thecom'bin'ationj of variable speed primary and movement-restrained secondary elements that are suitably supported for separate movement and have opposed closely-adj acent non-contacting friction vsurfaces; a liquid body partially filling the interspace between said surfaces, and thermowith active portions thereof, of a compenl sating liquid body communication with thev saidv interposed or. active one, and proportioned to vary the effective contact area of the acti-ve liquid 'approximately inversely to its temperature-e'ected viscosity changes.

6. The combination with freely movable-` ments, having friction surfaces in opposed,

closely-adjacent non-contacting relation, of n v means providing a reservoir, communicating with the interspace between said elements, and a liquid body having a reservoirfilling component and an Aactive-torquetransmitting component that normally, partly occupies said interspace, these components proportioned? volumetrically for temperature-edected change ofthe contact area of the.active component in approximately linv a temperature-compensating Spee indicator, the combination of a freely rotatable cylindrical cup; a cylinder-formed inverse ratio to the attendant changesof liquid viscosity.

member inthe upper portion thereof,A

the cup below the pivoted'member and eX- vpivoted and springrestralned; and a body of mercury lling the reservoir-portion of y tending partial-ly in the narrow interspace between-the cup and cylinder.'

llntestimony whereof lf ax my si ature. j 

